Logarithmic Scales in Acoustic Spectra: Decibels and Octaves

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In acoustics, huge changes in measurable physical parameters (pressure, power, frequency) correspond to relatively small changes in perceived properties (loudness, pitch). Simply using a linear scale is impractical, since the variation gives an inadequate guide to the perceived sound. Instead it is more practical to convert to logarithmic scales. Octaves are the logarithmic units for frequency, and decibels are the logarithmic units for pressure and power. Use this Demonstration to see the relationship between linear and logarithmic units in the spectra of different acoustic waveforms.

Contributed by: José Luis Gómez-Muñoz (June 2014)
Open content licensed under CC BY-NC-SA



An example of a waveform and its acoustic spectrum in decibels and octaves is found in [2].


[1] I. Drumm. "A Guide to Decibels and How to Use Them." (Jun 16, 2014) www.acoustics.salford.ac.uk/acoustics_info/decibels.

[2] MrAudioSoundImages. "Logarithmic Scale." (Oct 29, 2015) www.acousticscale.org/wiki/index.php/File:PRSandAcousticScale.pdf.

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